Field of the Invention
The invention pertains to the field of electric phasers (e-phasers). More particularly, the invention pertains to a tapered roller drive for an electric phaser.
Description of Related Art
In a closed loop power transmission system, variable cam timing (VCT) is the system that measures the angular displacement, or phase angle, of a camshaft, relative to the crankshaft to which it is operatively connected and then alters the phase angle to adjust various engine characteristics in response to demands for either an increase or a reduction in power. Typically, there is a feedback loop in which the desired values of such engine characteristics are measured against their existing values, and changes are effected inside the engine in response to any variances. To accomplish this, modern automobiles usually have one or more Electronic Control Units (ECU), which constantly analyze data from various parts of the engine or from other parts of the automobile, such as, for example, exhaust gas sensors, pressure sensors, and temperature sensors. A control signal is then emitted in response to such data. For example, with regard to VCT systems, as changes occur in engine or external conditions, the angular displacement between the camshaft and the crankshaft is adjusted accordingly.
A VCT system includes a cam phasing control device, sometimes referred to as a phaser, control valves, control valve actuators, and control circuitry. VCT is a process that refers to controlling and varying, when desirable, the angular relationship (the “phase”) between the drive shaft and one or more camshafts, which control the engine's intake and exhaust valves. An electric phaser (e-phaser) is driven by an electric motor to control and vary the angular relationship between the drive shaft and one or more camshafts. In response to input signals, the electric phaser adjusts the camshaft to either advance or retard engine timing.
Torotrak Ltd. (Leyland, Lancashire, England) produces a continuously-variable transmission (CVT) with steel discs and rollers in place of conventional toothed gears. A lubricating and traction fluid ensures grip for the transfer of torque between the rollers and discs.